The extent of the damage isn’t yet clear, and the grocery chains haven’t yet said how many customers might be affected. SuperValu said it knows hackers broke into the computer network that processes card payments, but it’s unsure whether they managed to take the data.

If they did, hackers made off with the typical information stored on a credit card’s magnetic stripe: your name, card number, expiration date and the three-digit security code.

SuperValu said the virtual break-in affected credit cards swiped at 228 stores between June 22 and July 17. Albertson’s did not say how many of its 1,060 locations were affected by the hack. But it believes more than 700 were affected.